Sedimentary Structures and Subfacies of a Mississippi River Point Bar

Abstract

Duncan point bar, Louisiana, can be divided into three subfacies of sedimentation, each characterized by-its unique combination of (1) sediment grade size, (2) assemblage of sedimentary structures, and (3) geographic position on the bar. These subfacies were deposited during one prolonged phase of high water between the levels of the maximum and minimum stands of the Mississippi. The efficacy of the bar's diversified primary sedimentary structures as either general or specific directional indicators of main stream flow is discussed. Interdigitating and erosive relationships between the subfacies indicate that during one phase of deposition the coarser-grained sediments are the last to arrive in the vicinity of the bar.